Two-phase-flow, panel-cooled, battery apparatus and method

ABSTRACT

Two-phase, boiling heat transfer in confined channels close to a source of heat, such as an electrical component or device, carries the latent heat of vapors away to remote locations where “real estate” demands of air convection are tolerable operationally, economically, and technologically. Liquid-to-vapor, phase-change, heat transfer in a narrow channel (e.g., typically less than 0.200 inches total thickness, and often less than 0.150 in the channel itself) improves by several hundred percent the heat extraction from modest temperature (e.g., about 120 degree F.) devices, when compared to heat fluxes in pool boiling. Saturated working fluids provide nearly isothermal conditions in the working fluid. Minimal conduction paths provide minimal temperature gradients, and capillary action may maintain nearly constant temperature conditions about a surface of a heat source, while carrying heat of vaporization away to a condensation location.

RELATED APPLICATIONS

This patent application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/167,019, filed: Apr. 6, 2009 and entitled TWO-PHASE-FLOW, PANEL-COOLED, BATTERY APPARATUS AND METHOD, which is incorporated herein by reference. Also, this patent application incorporates herein by reference U.S. patent application Ser. No. 11/743,555, filed on May 2, 2007 and U.S. patent application Ser. No. 12/417,552, filed on Apr. 2, 2009.

BACKGROUND

1. The Field of the Invention

This invention relates to heat transfer and, more particularly, to novel systems and methods for two-phase cooling of battery packs using comparatively modest temperature differentials.

2. The Background Art

A drawback and technical limitation of high-density populations of electronic components and chips is the difficulty of cooling. Electrical processes reject heat that must be carried away. With greater integration of electronic components, heat rejection cannot be taken for granted. Leaving components to reject heat to ambient air is insufficient in closed cases, potted assemblies, and the like. Likewise, convective heat transfer coefficients are comparatively poor in systems relying on air or gas environments. Conduction along common dielectric materials such as plastic potting materials is also especially poor.

Likewise in transformers, power electronics, batteries, and the like, carrying away waste heat is imperative for improved efficiency and life. Often, batteries and other systems are sensitive to the presence of extraneous electrical conductors. Voltage stress risers, dielectric breakdown, shorts, and the like must be avoided. Cooling electrical and electronic equipment is a paradox. Metals are the best thermal conductors, but also excellent electrical conductors, and may even have harmful magnetic properties of consequence.

What is needed is more compact heat exchange systems for electrical applications. An ability to tolerate high accumulated voltages developed along banks of battery cells may be imperative in a cooling system. Compact electrical components with minimal invasion by heat transfer components carrying heat away therefrom would be a substantial advance in the art.

BRIEF SUMMARY OF THE INVENTION

Although convective heat transfer coefficients in gas environments are comparatively poor compared to those in liquids, and extremely poor compared to those in boiling liquids, an apparatus and method in accordance with the invention may redistribute these functions. Conduction may be limited to very short paths. Boiling heat transfer may be located close to the source of heat. Mass transport may carry heated fluids away to remote locations where the “real estate” demands of air convection are tolerable operationally, economically, and technologically.

In view of the foregoing, in accordance with the invention as embodied and broadly described herein, a method and apparatus are disclosed in one embodiment of the present invention as including liquid-to-vapor, phase-change, heat transfer in a narrow channel. For example thicknesses may be less than an inch between adjacent heat generation plates or boards, often under half an inch for printed circuit boards, even less than a quarter inch in many cases, which may or may not include the thickness of two adjacent, planar, sources of heat generation and their intervening coolant channel.

For such devices, as well as batteries and the like, distances may typically be less than 0.200 inches total thickness, and often less than 0.150 in the coolant channel itself. Boiling heat transfer coefficients in narrow channels may be improved up to 800% at low heat fluxes over pool boiling. The fluid contained in the narrow channel system will be saturated, so the pressure inside the channel depends only on the boiling temperature of the fluid and its vapor pressure at that condition. In many cases, the pressure of the working fluid inside the channel may be less than atmospheric pressure. Because the fluid is saturated, the interior of the narrow channel will be nearly isothermal.

An apparatus for cooling one or more heat generating components may include a housing or panel to which the heat generating components may be mounted. A two-phase working fluid contained within that panel may then boil off vapors which may be returned to a condenser. Various piping may connect the panel to an external condenser. Likewise, in other embodiments, the panel itself may be sealed such that one portion of the panel boils off liquid working fluid into a vapor, which may then be converted back to a liquid by heat exchange in another portion of the panel, such as a portion of the panel equipped with fins, a liquid-to-liquid heat exchanger, or the like.

In alternative embodiments, the housing may be a sealed container having electrical components deployed on planar substrates, such as electronic components mounted on a printed circuit board, plates of a lithium-ion battery, or plates of some other battery system. The substrates may typically be arranged in banks or batteries of parallel, planar, walls with the working fluid free to pass completely around the components and substrates in intimate contact. For example, a dielectric coolant may eliminate the need for discrete panels to carry heat away from heat sources. Thus, the operational descriptions herein regarding enclosed, sealed panels, may be said, and is intended to apply, to banks of panels sealed in a single housing surrounding the entire bank or battery of heating panels.

Even concentric cylinders around cylindrical batteries can create the operation of bubble-scrubbing, enhancing free convection of liquids and vapors in a narrow channel.

One may think of a housing as including a sealed region containing saturated liquid and vapor of a working fluid. The housing may include many internal “walls” or planar substrates generating heat. Meanwhile, the housing may have walls sealed together to contain the working fluid. In certain embodiments, one dimension of a single unit (think of two walls and a cooling channel therebetween, which may be any two heating substrates or planar heat sources) may be comparatively smaller, e.g. on the order of 0.200 inches. The other two dimensions may be much larger dimensions (e.g. of from about 4 to about 18 inches) in the planar aspect of the panel, plate, wall, unit. The primary mode of heat transfer may be a liquid-to-vapor phase change. Boiling in a narrow gap causes much higher heat transfer coefficients than pool nucleate boiling. In one method and apparatus in accordance with the invention, the system may be hermetically sealed.

The housing or panel may include a fluid inlet and a fluid outlet. Therefore, heat generating components may be integrated directly against the outermost planar surfaces of the panels. The panels may provide structural support for the heat generating components by virtue of their own internal structure Likewise, the panels may be made of metal and may be hollow, maintaining their dimensions by interior pedestals. Thus, the panels may form a substantial part of the structure of an overall bank of heating walls, or other heat generating components such as electronics, batteries, or the like.

The heat exchange with the environment may be through an air-cooling radiator or through an alternative liquid cooling system. For example, a double loop heat exchanger may be used. Nevertheless, in certain embodiments, the space constraints may dictate air in proximity to the panels themselves, a remote heat exchanger, a condenser, a closed loop liquid cooling system that rejects heat remotely elsewhere to the environment, or the like.

In one embodiment, the heat exchangers may be located above the heat generating components and connected to the panels themselves. With this heat exchanger region of fins, or other heat exchanger receiving heat from the panels, the heat rejection may be in the upper portion of the panels, while below, the heat receiving portion of the panels receives heat from batteries, heat generating electronics, or the like. Thus, the heat exchanger located above the heat generating components relies on gravitational forces to return the heavier liquids while permitting the lighter vapors to rise toward the heat exchanger region of the rejection portion of the panel.

Alternatively, the fluid outlet at the top of the panel may release vapor, while a fluid inlet at or near the bottom of the panel may receive the condensed liquid for boiling again.

In certain embodiments, batteries in accordance with the invention may be maintained at about 50 degrees Celsius, about 120 degrees Fahrenheit, with a minimal total temperature differential (e.g. 2-10 degrees Fahrenheit) between the temperature of the battery, the working fluid, and the temperature of the working fluid at the heat exchanger rejecting heat. In certain embodiments, dielectric materials, plastics, various reinforced polymers, as well as metals may be used for forming the panels. Nonmetallic housings may be used for forming the panels. Thus, these may be used within a magnetic field without affecting the magnetism, or magnetic flux Likewise, if not magnetic, the panels may then not tend to draw the magnetic flux or be exposed to eddy currents generated thereby.

In certain embodiments, the working fluid may be a dielectric fluid. Nevertheless, water is an excellent working fluid in many environments. Where a battery component is sealed, neither dielectric coolants nor dielectric panels may required. In other embodiments, the entire working fluid and these mechanical containment and heat transfer panels may need to be made of a dielectric material.

In currently contemplated embodiments, the two-phase working fluid is maintained substantially pure. Any time a mixture of materials is permitted, the possibility and probability of preferential evaporation may cause difficulties in operation Likewise, small amounts of non-condensibles may also be found in liquids. It is important to remove non-condensibles, because at equilibrium they will come out of solution again.

In one embodiment, a loop setup may provide for a remote condenser. This may assist in reducing the frictional and entrainment losses in the apparatus Likewise, the difficulty of vapors at comparatively higher volumes passing through liquids at comparatively lower volumes has the added problem of entrainment, trapping, drying out, and the like in certain environments.

Reduced pressure losses may provide for a substantially isothermal operation of each panel. Since two-phase heat transfer is used, most of the heat is transported by the latent heat of the operating fluid. By suitable selection of operating fluids, temperatures well below ambient freezing may be used. Alcohols, ether, refrigerants, and the like will serve in such environments without freezing.

The temperature of the working fluid may be controlled by changing the flow of the external fluids through the heat exchanger external to the panel. Due to the buoyancy and resulting column pressure differential between the heat absorbing portion of the panel and the heat rejecting portion of the panel connected to the external heat exchanger, the flow of the working fluid may operate by substantially free convection, although restricted within a confined space. In certain embodiments, the apparatus may operate substantially passively. Likewise, the system may be pumped but need not be. Even with an external heat exchanger located remotely from the panels, free convection may control the two-phase transport processes.

In other embodiments, the heat generating components, such as batteries or printed circuit boards may be immersed in the working fluid. However, if the heat generating components are unsealed electronic components or batteries, then the working fluid may need to be a dielectric material. If the coolant channels are sealed away from the heat generating planar components (e.g., batteries, plates, circuit boards, etc.) then the coolant may be sealed in a metal envelop conducting to such planar components. Otherwise, a housing may hold the entire array of heat sources in an open pool of fluid, all sealed within the housing and any associated heat exchange loop.

The heat generating components may be coated with a thin dielectric coating or seal if the working fluid is not to be dielectric. Of course, sealing, testing, and protecting against damage or penetrations of the dielectric coating may be required. However, so long as there is not a problem with magnetic or electric connections with the working fluid, the working fluid may actually be water or some other material that is not dielectric.

If coatings are used on the heat sources, then it may be important to render them as thin as possible in order to minimize the length of the conductive path for heat. Thus, the thinner the conductive path, the less resistance to heat flow in the apparatus.

In certain embodiments, the working fluid may completely fill the panel. The working fluid as a liquid substantially filling the cooling channel between adjacent heating plates, or within a sealed, standalone, coolant panel, may be appropriate. In other environments, a substantial amount of vapor may exist in the liquid as a result of the confined-channel, boiling, heat-transfer processes in accordance with the invention.

Hereinafter, one may consider a “panel” to be either a sealed panel, located between and carrying heat from two adjacent, planar, heat sources or simply to be any two “walls” or planar sources of heat with an intervening channel of working fluid cooling both. Of course, in this latter configuration, each of the adjacent, planar, heat sources may also be partially cooled by another channel located on the opposite side from that of the channel shared with each other.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the present invention will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only typical embodiments of the invention and are, therefore, not to be considered limiting of its scope, the invention will be described with additional specificity and detail through use of the accompanying drawings in which:

FIG. 1 is a perspective view of one embodiment of a two-phase cooling panel in accordance with the invention, and cooled using an upper, finned section; FIG. 2 is a perspective view of the apparatus of FIG. 1 ganged together in a collected assembly;

FIG. 3 is a perspective view of the apparatus, such as that of FIGS. 1 and 2 or of a bank of planar-walled heat sources in a single contained pool, illustrated here as battery packs, such as lithium ion battery cells, wherein generated heat is transferred away by panels in accordance with the invention;

FIG. 4 is a perspective view of an alternative embodiment of a panel, in accordance with the invention, in which a panel is open to discharge vapor from the top thereof and receive a return flow of liquid at a lower point thereon;

FIG. 5 is a front elevation view of one embodiment of a panel of FIG. 4 connected to an outlet line carrying vapors to a condenser, sometimes referred to as a radiator, being a finned heat exchanger discharging heat to the environment, the apparatus then returning liquid working fluid back through a return line to a lower point on the panel of the invention;

FIG. 6 is a perspective view of an alternative embodiment of a panel in accordance with the invention connected to other panels operating in a horizontal plane, whereas the principal panel works in a vertical plane, the apparatus in this configuration providing either solid or a hollow two-phase heat transfer working fluid connecting either by a solid connection or by a fluid connection, or both to the central and principal vertical panel, which then discharges vapors into a vapor line carrying the vapors toward a condenser;

FIG. 7 is a perspective view of the apparatus of FIG. 6 provided with heat sources, here represented by lithium ion batteries or the like connected to the horizontal panels, which in turn discharge or reject their heat into the central vertical panel, feeding heated vapors into the vapor line for transport to a condenser which will eventually return liquid to a liquid line feeding the principal panel;

FIG. 8 is a perspective view of the apparatus of FIG. 7 connected together in multiple banks of cooling panels connected to a vapor discharge line;

FIG. 9 is a front elevation view of the assembly an apparatus of FIG. 8; and

FIG. 10 is an end elevation view of the apparatus of FIGS. 7, 8, and 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It will be readily understood that the components of the present invention, as generally described and illustrated in the drawings herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the system and method of the present invention, as represented in the drawings, is not intended to limit the scope of the invention, as claimed, but is merely representative of various embodiments of the invention. The illustrated embodiments of the invention will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout.

Referring to FIG. 1, a single (either open-pool, or hermetically sealed) narrow channel may receive heat into a working fluid. The narrow channel in this case may be filled completely or only partially with liquid, allowing for vapor to exit from or to re-condense in an upper portion thereof. Heat generating components may be, or be attached to, the outer surfaces of the lower portion of the narrow channel. Heat leaves the panel via transfer by the working fluid into and then convection out of the fins in the top portion of the channel, or of a containment housing. The top portion may be a condenser section. The condenser section in such an arrangement is typically above the lower, boiling, section in the gravity field. The fins may be made from a hollow or solid heat-conductive metal such as aluminum. The channel may be formed in an open or closed configuration, from a variety of materials including metals, plastics, and composite materials.

In the apparatus 10 of FIG. 1, a panel 12 may be disposed in a vertical orientation, or angled to have a sloped position. Alternatively, a separate conduit may return condensate to the lower portion of any panel. Again, note that a panel may be closed, and located between to heated plates, substrates, etc., or may be two, open, heating walls having a passage therebetween for the operating fluid to cool both. In this way, the panel 12 is able to rely on the effects of gravity to return the heavier liquid phase of a material, upon condensation in the upper portion 14 of the panel 12. Thus, upon heating in the lower portion 16, of the panel 12, a vapor will develop and rise to the upper portion 14.

The upper portion 14, being provided with fins 18 or other cooling mechanisms 18 will condense the vapor phase of the working fluid. Upon condensation, the heavier liquid returns back to the lower portion 16 of the panel 12, either by a conduit, or within a free, open pool contained in the housing for the bank of panels.

In certain embodiments, such as sealed panels between heat sources, the working fluid may be water. However, alcohol, ether, various refrigerants, dielectric fluids, and the like may be considered as suitable working fluids operating in two phases within a sealed or open panel 12. In general, one embodiment of a panel 12 may be formed as disclosed in the patent applications incorporated herein by reference. The details, being explained therein, will not be repeated here. Nevertheless, the panel 12 may be a hollow panel having an overall thickness of from about 0.050 inches to about one half inch in thickness. One embodiment, having an overall thickness of about 0.200 inches with a resulting cavity of about 0.80 inches in thickness, has been found well suitable. Alternatively, the planar sources of heat may form adjacent walls of a panel, open to a pool of working fluid, the heat sources and the working fluid all being contained within a sealed housing, whether or not serviced by additional condensers, intervening conduits, or both.

Typically, the overall planar dimensions of a panel 12 may be from about 8 to about 12 inches in width, and about 12 to 18 inches in height. This particular size is suitable for banking together several hundred lithium ion batteries suitable for producing the power required to drive an automobile or other street-legal vehicle. In one embodiment, battery panels of about one quarter inch thickness may fit against, or may themselves form, the panels 12, below the fins 18. Accordingly, the fins may extend in length away from the panel 12 a distance of from about one eighth inch to about two inches. Nevertheless, in the embodiment of FIG. 2, the fins 18 may accommodate neighboring fins 18 of neighboring panels 12.

Referring to FIG. 2, an array of the narrow channels has a top portion that may be viewed as a radiator, which may actual perform as a radiator, a convector, or both. This may be scaled to any size to accommodate a variety of heat generating components.

In general, numerous panels 12 may be banked together in an array. The lengths or the extension distance of the radiators 18 away from the face of the panel 12 may be selected to accommodate the intervening spaces between the panels 12 that will eventually hold the heating sources.

Referring to FIG. 3, heat generating components, such as lithium ion batteries may be attached to or placed in intimate thermal contact with the lower portion of the thin panels 12. Batteries in accordance with an apparatus and method of the invention may typically be on the order of about 4 inches by 6 inches in extent with a thickness of about ¼ inch. Of course, other sizes may be manufactured much larger or much smaller than the foregoing. Nevertheless, for automotive applications, it is considered that such sizes of cells may produce the proper amount of current, voltage, and heat suitable for integration into an apparatus 10 in accordance with the invention. Thus, the batteries 20 may be arrayed in alternating, intimate contact with, or forming the very walls of, any of the panels 12. Thus, the heat generated by the batteries, typically on the order of about 10 watts per cell may eventually generate about 3,000 watts in a battery assembly suitable for automotive applications.

In the embodiment of FIG. 3, the panels 12 are filled and sealed such that saturated liquid and vapor coexist within the interior of the panels 12. The panels 12 may be formed exactly as described in various embodiments shown and described in the patent applications incorporated herein by reference. Thus, pedestals within the panels may space the sides of the panels 12 apart. Likewise, the pedestals may maintain the dimensions of the panels 12 without expansion nor collapse of the sides away from or toward one another. Likewise, the channels between the pedestals, although thin, normal to plane, may be comparatively narrow or extremely wide in-plane. In certain embodiments, periodic pedestals may simply be spaced at an appropriate distance to maintain dimensionality while leaving almost the entire interior of each panel 12 open for the transport of fluid. In a vertical configuration, where capillary action is not relied upon to return liquid from the vapor region to the liquid region, the number and size of the pedestals may be dictated entirely by dimension stability requirements.

Structural needs to prevent collapse or expansion of the thickness of the panels may be controlled by the pedestals. Nevertheless, in other configurations, where the panels 40, or some other related panels may be connected thereto in a horizontal direction, capillary action of the panels 12 is appropriate. The channels and supporting pedestals therebetween may be sized accordingly as described in the patent applications incorporated herein by reference.

Alternatively, each panel 12 may simply be considered a channel of fluid with its two adjacent “walls.” Walls may be formed by any heat sources such as batteries or arrays of components mounted on printed circuit boards and either completely or partially submerged inside a sealed, containment housing.

Referring to FIG. 4, another embodiment of an apparatus and method in accordance with the invention may rely on the narrow channel substantially completely filled with liquid. The fluid is maintained in a saturated state, so any additions of heat will cause phase change. Vapor exits the top of the narrow channel, where it is transported to an external radiator, condenser, or the like. The condensed liquid is then returned from the external radiator to the bottom of the narrow channel. The radiator is typically oriented above the narrow channel in the gravity field.

Referring to FIG. 4, and generally to FIGS. 4-10, one embodiment of a panel 12 in accordance with the invention may provide a vapor port 22 connected to a header 24 collecting vapor from the panel 12. For example, in the illustrated embodiment, the lower portion 16 of the panel 12 is substantially the entire expanse of the panel 12. Thus, the lower portion 16, of the panel 12 feeds vapor boiling from the sides thereof inside the cavity or channel of the panel 12 into the header 24.

The header expands to a larger opening to consolidate and promote flow of the vapors from the various panels 12 for transport out through the exit port 22. The exit port 22 or vapor port 22 may pass the vapors to a condenser for return as liquid to the liquid port 26.

Referring to FIG. 5, a modular cooling unit may include a narrow channel in the center. Fins extending from the narrow channel may be either solid or hollow. In the case that the fins may be hollow. The interior of the fins may be open to the narrow channel, allowing for the fins and the narrow channel to all be nearly isothermal. Heat-generating components may be attached to the fins. The fins may act as a channel to transfer heat from the heat generating components to the narrow central channel.

In the illustrated embodiment, the exit port 22 of a panel 12, and particularly the lower portion 16 thereof, feeds vapor into a line 28 or vapor transport line 28 feeding into a condenser 30. The condenser 30 may be of any suitable type. For example, radiators and condensers used in heating, ventilating, air conditioning, and automotive uses, and so forth may also serve in this role. By virtue of condensation in the condenser 30, liquid is returned into a return line 32 feeding into the inlet port 26 of the panel 12. Referring to FIG. 6, heat generating components such as lithium ion batteries may be attached to the apparatus of FIG. 5. Bonding, thermal grease, or other intimate contact may improve conduction heat transfer.

In the illustrated embodiment, the principal panel 12 is arranged vertically. Meanwhile, additional panels 40 may operate in a horizontal orientation. The panels 40 may be solid conductors, identical hollow panels 12 like the principal pane112, or may be capillary-driven two-phase heat transfer panels as described in detail in the patent applications incorporated herein by reference.

In some embodiments, adjacent walls of heat-generating, planar configuration may promote nucleate boiling at various locations thereon. For example, choosing a working fluid and an operating pressure permits one to choose the operating temperature of the operating fluid cooling the walls. As bubbles rise, in a confined space between those walls, they will grow. Regardless, those bubbles, especially if closely confined, will scrub the surfaces of the walls as the bubble pass upward under the influence of gravity. The confinement distance or spacing between walls is a design parameter to be determined by controlling factors, such as the height of a panel, the material properties of the working fluid, and the amount of heat being transferred to the working fluid, in order to promote the scrubbing effect.

One of the benefits of this open pool type of operation is that nucleate boiling may be augmented by bubbles passing by, thus promoting re-flooding of a location that might otherwise become covered by vapor and thus reduce its effective heat transfer rate to the vapor phase of the working fluid. By contrast, promoting a close proximity of the walls, with greater distances in height, may create a chimney of bubbles vigorously scrubbing the adjacent walls on each side in order to promote stripping of the bubbles forming thereon, with immediate, corresponding re-flooding by liquid phase working fluid.

The panels 40 may be connected as sealed units having only a solid mechanical , conducting interface with the panel 12. Alternatively, walls may have intimate thermal contact with the working fluid. Also, in some embodiments, the panels 40 may connect to, and share a working fluid with, the panel 12, or a sealed housing containing immersed panels 12. Thus, the panels 40 may carry liquids toward hotter regions by capillary action, or may scrub vigorously the adjacent “pool mounted” walls of a panel 12, and return vapors back out through channels toward the principal panel 12. Thus, the line 28 connected to header 24 of the principal panel 12 may carry vapor collected from the panel 12, or from all the panels 40 into the panel 12 for transport to a condenser 30 remote therefrom.

Suitable connectors 36, including various fittings, seals, welds, and the like may provide a vapor and liquid seal connecting the header 24 of the panel 12 to the line 28.

Referring to FIG. 7, two of the modular sections shown in FIG. 6 connect together. The modularity of the system allows for very simple scaling. As seen in FIGS. 7-10, a bank of the panels 40 may host heat sources such as batteries 20 in intimate contact with each of the panels 40. Again, the panels 40 may be solid conductors, two-phase, heat-transport panels as described hereinabove, systems described in the patent applications incorporated herein by reference, or any combination thereof

In the illustrated embodiment, the batteries 20 may reject heat into the panels 40. The panels 40 may reject heat into the central or principal panel 12. The panel 12 through its header 24 may pass vapors into the line 28 for delivery into a condenser 30. The condenser 30 returns liquid working fluid back to the inlet port 26 of the panel 12.

Referring to FIGS. 8-10, an apparatus 10 in accordance with the invention may be ganged in multiple banks of battery units. As illustrated, various configurations may require ganging multiple units of the apparatus of FIG. 7. In the illustrated embodiment , multiple panels 12 may be ganged together on a line 28 acting as a collector. Meanwhile, the various batteries 20 or other heat sources 20 feed heat into the panels 40, which heat is rejected into the panels 12. Meanwhile, the vapors are carried in the line 28 to the condenser 30 for condensation and heat rejection to the environment.

The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope. 

1. A method of heat removal comprising: providing a source of heat; providing a first panel comprising a wall containing a single working fluid operating in two phases; passing heat from the electrical component into the wall; passing heat from the wall into the working fluid; forming discrete bubbles of vapor by boiling the working fluid at the wall; rising by some of the discrete bubbles; sweeping others of the discrete bubbles of the vapor from the wall by the some of the discrete bubbles; condensing the vapor to a liquid; and returning the liquid to proximate the source of heat.
 2. The method of claim 1, wherein the source of heat is an electrical component generating heat losses.
 3. The method of claim 2, wherein the working fluid is dielectric.
 4. The method of claim 1, wherein the wall is vertical, the method further comprising connecting a second panel to the first panel in mutually orthogonal relation.
 5. The method of claim 4, further comprising sharing by the first and second panels a common working fluid.
 6. The method of claim 5, wherein: the wall is planar; the second panel extends parallel to a plane orthogonal to the wall.
 7. The method of claim 6, wherein the second panel is oriented horizontally and carrying heat horizontally from the heat source to the first panel.
 8. The method of claim 7, further comprising carrying, by a line connected to the first panel, a vapor phase of the working fluid from the first panel to a condenser.
 9. The method of claim 8, further comprising returning a liquid phase of the working fluid to the first panel from the condenser.
 10. The apparatus of claim 1, wherein the panel is sealed to contain exclusively the working fluid, the method further comprising: providing a heat exchanger removing heat from the first panel by conduction; the first panel boiling the liquid phase of the working fluid to vapor and condensing the vapor phase of the working fluid to liquid.
 11. An apparatus comprising: a source of heat; a working fluid operating at saturation temperature and pressure; a first panel comprising a first wall exposed to the working fluid in two phases; the first panel, further comprising a second wall spaced from the first wall and parallel thereto; the working fluid contained to be free to convect in a space between the first and second walls, the space between the first and second walls being about an order of magnitude less than the planar dimensions thereof; at least one first source in intimate contact with the first wall and exposed to conduct heat into the working fluid; at least one second source in intimate contact with the first wall and exposed to conduct heat directly into the working fluid; the first wall spaced from the second wall a distance selected to form first discrete bubbles of vapor by boiling the working fluid at the wall; the first and second walls forming second discrete bubbles above the first discrete bubbles, and the first discrete bubbles sweeping the second discrete bubbles away from the first and second walls by rising along and expanding against the first and second walls; and a condenser receiving a flow of vapor comprising the content formed of the coalescing of the first discrete bubbles and the second discrete bubbles, to condense the flow from the vapor phase back to the liquid phase.
 12. The apparatus of claim 11, further comprising a first line returning the liquid to proximate the source of heat.
 13. The method of claim 12, wherein the source of heat is an electrical component generating heat losses and the wall is a mounting surface supporting the electrical component.
 14. The apparatus of claim 13, wherein the working fluid is dielectric.
 15. The apparatus of claim 14, wherein the first and second walls are vertical, the apparatus further comprising a second panel connected to the first panel in mutually orthogonal relation.
 16. The apparatus of claim 15, further comprising an open connection between the first and second panels, sharing between the first and second panels the working fluid as a common working fluid.
 17. The apparatus of claim 11, wherein: the wall is planar; the second panel extends parallel to a plane orthogonal to the wall.
 18. The apparatus of claim 17, wherein the second panel is oriented horizontally and carrying heat horizontally from the heat source to the first panel.
 19. The apparatus of claim 11, wherein the apparatus is sealed to contain and maintain uncontaminated the working fluid, the apparatus further comprising: the first panel comprising a lower portion containing a boiling, liquid phase of the working fluid, evaporating to vapor; the first panel comprising an upper portion condensing the vapor phase of the working fluid to liquid; and a heat exchanger removing heat from the vapor phase of the working fluid.
 20. The apparatus of claim 11, wherein the first source is selected from an electrical component on the first wall operating as a circuit board, a battery, and another chemical heat generator. 